Digital image capture has received widespread acceptance by users of image capture equipment. Both still and video digital cameras, which use solid-state imagers or image sensors to capture images, are presently in widespread use. Common solid-state imagers, which have an array of pixels for image capture are based on CCD and CMOS technology, as well as others.
Color imagers typically output red/green/blue (RGB) color signals from a pixel array, since each imager pixel is typically covered by one of a red, green, or blue filter; arranged, for example, as in a conventional Bayer pattern, illustrated in FIG. 1. A Bayer pattern includes alternating rows with one row having alternating green pixels 20 and red pixels 20, and the next row having alternating blue pixels 20 and green pixels 20. This pattern repeats for the entire array 10. Imagers also exist which output monochromatic signals from a pixel array.
One problem confronted by solid-state imagers is the presence of noise in the captured image, particularly under low-light conditions, and/or where an ISO setting of a camera is set high, resulting in shorter image integration times. Image noise appears in a displayed or a printed image as a graininess in the image.
As pixels get smaller, more pixels are possible in a given area of silicon. This satisfies the market desire for higher resolution imagers at the same optical format. However, for the same amount of light striking the imager array, each of the pixels receives correspondingly less signal. This results in an apparent signal-to-noise ratio (SNR) reduction for the overall picture, often perceived as a reduction in overall low-light sensitivity and image quality. Because of this, conventional thinking is that smaller pixels are less desirable for low-light applications.
Accordingly, there is a need and desire for better images with improved signal-to-noise ratios for imagers with small pixels.